Genetic parameters of vulva traits and impact of vulva scores on gilts culling in Large White pigs

Vulva morphologies represent significant traits in pig production. Recent studies suggest that vulva size can be predictive of the reproductive performance of gilts. This study aimed to analyse the genetic parameters of vulva traits, including vulva length, vulva width, and vulva angle score (VAS), as well as litter traits, including total number born, number born alive, number stillborn, and piglet survival rate, across three Large White pig strains (PIC, Topigs, and Canadian). We estimated the correlations between vulva traits and litter performance, as well as the reasons for culling gilts. In this study, single-trait and multitrait models were employed to estimate the heritability and genetic correlations between vulva and litter traits. The heritabilities of vulva traits ranged from 0.167 to 0.426, whereas the heritability of litter traits ranged from 0.013 to 0.147. The VAS in Topigs Large White pigs exhibited the highest heritability. The genetic correlation coefficients between vulva length and width in PIC and Topigs Large White pigs were significantly positively correlated, ranged from 0.585 to 0.767. No significant correlation was found between vulva and litter traits. Subsequently, we scored the vulva traits according to previously reported studies, linear relationship analysis between vulva score and reasons for culling gilts revealed that gilts with larger vulva widths had a lower risk of culling. The average vulva width score of the gilts that were culled due to prolonged oestrus was significantly lower (2.75) compared to that of gilts with normal oestrus (2.90). In the population of gilts aged 220-230 days, the gilts with higher vulva angle scores had a lower risk of culling due to vulva inflammation with purulent discharge. The results suggest that selecting vulva traits in replacement gilts is an effective strategy to reduce gilt culling rates.